Walk reel mowers are known for precision cutting of grass and the like, such as the grass found on golf greens. Such reel mowers typically have a frame which carries a reel cutting unit. A handle assembly extends upwardly and rearwardly from the frame to allow an operator who walks behind the mower to guide and operate the mower. The handle assembly includes various controls for allowing the operator to selectively engage and disengage the traction drive of the mower as well as the reel cutting unit.
Prior art walk reel mowers are known in which the reel cutting unit is carried rigidly on the frame, like that shown in U.S. Pat. No. 5,477,666 to Cotton or U.S. Pat. No. 4,481,757 to Tsuchiya. Such a cutting unit does not pitch, roll or yaw relative to the frame to adapt itself to the contours of the ground. When this mower cuts grass on an undulating surface, it is quite possible to scalp or scuff the grass. For example, the grass might be cut too closely on top of a high spot and not closely enough in a low spot. This is undesirable.
Other reel mowers, such as that shown in U.S. Pat. No. 2,972,218, disclose walk reel mowers having a “full floating cutting unit” that can move in three degrees of freedom relative to the mower frame. This is done by making the cutting unit self-supporting on its own front and rear rollers. The cutting unit is then suspended from the mower frame by a set of chains that are normally slack when the cutting unit is in engagement with the ground. The slack chains allow the cutting unit to move relative to the mower frame to better follow the contours of the ground to minimize instances of scalping and/or scuffing and to help provide a more consistent height of cut.
While the ground contour following characteristics of a reel mower are not possessed by a reel mower with a cutting unit that is rigid with the frame, the use of chains to support  the cutting unit provides disadvantages of its own. When the operator pushes down on the handle assembly to raise the front end of the reel mower, the cutting unit does not immediately lift up off the ground. The chains first have to tighten before the cutting unit lifts up off the ground. Thus, when pushing down on the handle to lift the cutting unit off the ground, the operator first feels a smooth motion while the chains tighten and then feels a jerk or discontinuity when the operator suddenly has to push down harder to get the cutting unit to come up.
The jerk or discontinuity felt by the operator in the handle as the operator pushes down on the handle to raise the cutting unit is a disadvantage. Most operators prefer cutting units in which one can push down on the handle to raise the cutting unit and this can be done in a smooth motion with the cutting unit raising immediately. This is simply not possible with cutting units suspended by chains that must be tightened before the cutting unit rises.
U.S. Pat. No. 2,329,952 to Speiser discloses a walk reel mower in which a reel cutting unit is mounted on the rear of the mower frame. However, the cutting unit has a floating capability in that the cutting unit can pitch and roll relative to the frame by virtue of transverse and longitudinal pivots between the cutting unit and the mower frame. While this provides a ground contour following ability without using slack chains to support the cutting unit, pushing down on the handle assembly will not lift the cutting unit off the ground. Thus, the mower shown in the Speiser patent is much more difficult to maneuver than the reel mowers described earlier.
In addition, the cutting unit shown in the Speiser patent is not itself totally self-supporting on the ground, but relies on the traction wheels of the mower frame in conjunction with a roller on the cutting unit for proper ground engaging support. As a result, the fore-and-aft wheelbase  of the mower is relatively large. This decreases how effectively the cutting unit will pitch when encountering transverse bumps or undulations in the ground, i.e. bumps or undulations that are perpendicular to the forward direction of motion. If the bump is small enough, the traction wheels may clear the bump before the cutting reel/bedknife interface reaches the high spot of the bump, thus still resulting in scalping.
Another problem with prior art walk reel mowers is the nature of the drives or transmissions used to power the traction drive and the cutting reel. Often, separate drives housed in separate gearboxes are used, one gearbox powering the traction drive and the other gearbox powering the cutting reel. The use of two gearboxes increases expense as well as requiring sufficient space on the mower frame for housing both gearboxes. In addition, the use of two gearboxes gives the mower a cluttered appearance.
Moreover, in many prior art walk reel mowers, a differential is needed to allow the left and right traction wheels, or the left and right traction drum halves, to rotate at different speeds when turning. In many prior art mowers, particularly those having a traction drum formed from traction drum halves including a left traction drum half and a right traction drum half, the differential was not carried in the speed reducing gearbox, but was instead built into the interior of the traction drum. In this location, it was difficult to keep the differential sealed and lubricated, and repair or replacement of the differential was also difficult. Moreover, any leakage of the lubricant from the differential out of the traction drum is problematic as such a lubricant can easily kill or mar the grass or turf being cut by the mower.
Some attempts are disclosed in the art to integrate the drives for the cutting reel and the traction drive into a single gearbox. One such attempt is shown in U.S. Pat. No.  1,709,791 to Jerram, in which the speed reducing gear drives used to power the traction drum and the cutting reel are housed in a common gearbox or gearcase that is built into one of the side plates of the reel mower frame. The clutches used to initiate operation of the drives for the traction drum and the cutting reel are also both housed in this common gearbox. Thus, this mower has only a single gearbox for enclosing both the traction and cutting reel drives, thus having a less cluttered appearance than mowers using multiple gearboxes.
Despite the attempt at simplification shown in the Jerram patent, various deficiencies are still present. For example, the differential for the traction drum is still housed within the interior of the traction drum. This gives rise to the lubricating and lubricant leakage problems discussed above. In addition, the overall drive and differential systems disclosed in Jerram involve the use of a large number of components, which leads again to increased cost.
In reel mowers in which the cutting unit floats to follow the contours of the ground, the drive to the cutting reel has to flex, bend and axially extend and contract to accommodate the floating motion of the cutting unit. In some mowers, such as that shown in the Speiser patent referred to above, this is accomplished using a flexible drive belt extending from one sprocket or pulley on the mower frame to another sprocket or pulley on the cutting unit. It is a problem with such a drive in keeping the belt taut as the cutting unit and mower frame move relative to one another. In addition, flexing or twisting of the drive belt is quite hard on the belt leading to relatively short belt life.
Other non belt type drives are known for the cutting reel. For example, flexible shafts are known for accomplishing this drive with one such shaft shown in U.S. Pat. No. 2,191,135 to Roth. This shaft comprises two universal  joints at either end connected by relatively slidable shaft sections. The shaft sections have mating, noncircular cross-sectional configurations to allow torque to be transmitted while the shaft sections slide in and out relative to one another. See FIGS. 7 and 9 of Roth.
While flexible shafts are known for powering floating cutting units, they must be lubricated to function quietly and properly and to have adequate life. Again, having to lubricate a flexible drive shaft to the cutting reel is a problem because such a flexible drive shaft is generally exposed and located above the cutting reel. Thus, the lubricant for the drive shaft or the universal joints at either end can leak and drop down onto the grass or turf, thus damaging the grass or turf. As in the case with leakage of the lubricant from a drum carried differential, this is not desirable.
In many prior art walk reel mowers, the controls used to place the traction drive and cutting reel in operation are separate from one another. In many cases, the control for operating the cutting reel is not carried on the handle assembly, but is located down on the mower frame adjacent the cutting reel itself. The other control for operating the traction drive is located up on the handle assembly. Such a dual control system, with the cutting reel control being down on the mower frame while the traction drive control is on the handle, is shown in U.S. Pat. No. 1,947,117 to Stegeman.
This prior art control system is disadvantageous as it is relatively cumbersome to start and stop the cutting reel. For example, to start and stop operation of the cutting reel, the operator has to walk from behind the handle assembly to a position around in front of the handle assembly in order to reach the control that starts or stops the drive to the cutting reel. After the operator manually actuates this control, the operator must then walk back behind the  handle assembly to continue operation of the mower. This back and forth walking motion is obviously inconvenient and tiring to do. As a result, the operator tends to leave the cutting reel in operation even at times when the cutting reel should otherwise be shut off.
In some prior art mowers, such as that shown in the Speiser patent referred to above, the controls for the traction drive and cutting reel are both carried on the handle assembly. At least in this device, the controls can both be reached and operated by the operator without having to walk around in front of the handle assembly. However, two separate controls are still provided, each with its own handle and control linkage. As such, the controls can be somewhat confusing to use as the operator must remember which control operates which item. Moreover, the use of separate controls again unduly clutters the handle assembly.
In walk reel mowers, it is common to collect grass clippings in a grass collection basket mounted to the mower frame so that the basket is positioned in front of the cutting unit. Sometimes, when the operator lifts up on the handle assembly of the mower when maneuvering the mower, it is possible for the grass basket to become disengaged from the mower. This requires that the operator walk around and reattach the basket to the frame. If the basket is partially filled with grass clippings, this can be difficult to do. Even if it can be done, it is inconvenient for the operator to have to reattach the grass basket.
Finally, in many reel mowers, whether they be walk reel mowers or riding reel mowers, it is common to pivot the bedknife towards the cutting reel to compensate for wear in the cutting reel. This has the effect of longitudinally moving the front edge of the bedknife from the position it occupies when the cutting reel is not worn. For example, in a cutting reel with a relatively unworn reel, the front edge of the bedknife might typically be behind the center of the  cutting reel by a certain amount. When the reel wears and the bedknife is pivoted up to maintain proper clearance to the cutting reel, this behind the center distance will change.
The Applicants have found that this change in the behind the center distance of the bedknife affects how aggressively the cutting reel cuts. Thus, after the reel becomes worn and the bedknife is adjusted in the manner just described, the cutting unit will cut differently than when the reel was new and the bedknife had not been adjusted from its initial orientation. This change in the quality of the cutting is not desirable. It would be best for the cutting unit to cut approximately the same regardless of how worn the cutting reel has become and whether or not the bedknife has been adjusted to compensate for this wear.